Method and device for controlling construction machine

ABSTRACT

A control method and apparatus for construction machine. A joint type arm mechanism is provided on a construction machine which is driven by a cylinder type actuator, which is itself connected to a fluid pressure circuit having a pump. The cylinder type actuator&#39;s delivery pressure is variable in response to the movement of an operation member and is operated by the delivery pressure from the pump. The delivery pressure of the pump is maintained greater than or equal to a predetermined value even when the operation member is in a neutral position for the cylinder type actuator, so that, even immediately after the movement of the arm mechanism is initiated, a response delay of the pump or an increase of the dead zone can be suppressed and the accuracy of the completed movement of a working member can be enhanced.

TECHNICAL FIELD

This invention relates to a construction machine such as a hydraulicexcavator for excavating the ground, and more particularly to a controlmethod and a control apparatus for a construction machine of the typementioned.

A construction machine such as a hydraulic excavator has a constructionwherein it includes, for example, as schematically shown in FIG. 13, anupper revolving unit 100 with an operator cab (cabin) 600 provided on alower traveling body 500 having caterpillar members 500A, and further, ajoint type arm mechanism composed of a boom 200, a stick 300 and abucket 400 is provided on the upper revolving unit 100.

And, based on expansion/contraction displacement information of the boom200, stick 300 and bucket 400 obtained, for example, by stroke sensors210, 220 and 230, the boom 200, stick 300 and bucket 400 can be drivensuitably by hydraulic cylinders 120, 121 and 122, respectively, toperform an excavating operation while the advancing direction of thebucket 400 or the posture of the bucket 400 is kept fixed so thatcontrol of the position and the posture of a working member such as thebucket 400 can be performed accurately and stably.

By the way, in such a conventional hydraulic excavator as describedabove, when an operation (raking) of moving a top of the bucket 400linearly such as, for example, a horizontal leveling operation isperformed automatically by a controller, solenoid valves (control valvemechanisms) in a hydraulic circuit which supplies and discharges workingoil to and from the hydraulic cylinders 120, 121 and 122 areelectrically feedback controlled to control the expansion/contractionoperations of the hydraulic cylinders 120, 121 and 122 to control thepostures of the boom 200, stick 300 and bucket 400.

In this instance, the hydraulic cylinders 120, 121 and 122 are connectedto the hydraulic circuits and are operated by a delivery pressure from apump, and when an operator operates an operation lever, supply ordischarge of the working oil to or from the hydraulic cylinders 120 to122 is performed through the hydraulic circuit so that the boom 200,stick 300 and bucket 400 operate.

And, immediately before driving of the joint type arm mechanism isstarted, the operation lever is disposed in a neutral position(non-driving position), and the pump mentioned above is in a condition(idling condition) wherein it little delivers the working oil. If theoperation lever is operated from the condition described, then thedelivery pressure of the pump gradually rises in response to theoperation amount of the operation lever.

Consequently, immediately after the operation lever is operated from theidling condition of the pump to start automatic control (immediatelyafter driving is started), since the delivery pressure of the pump doesnot exhibit a sufficient rise, a response delay of the pump occurs, andbesides, due to the fact that the pump load is lower than the loads tothe hydraulic cylinders 120 to 122, the dead zone is increased,resulting in deterioration of the posture control accuracy of the bucket400. Accordingly, it is difficult to improve the finish accuracy of ahorizontally leveled surface or the like by the bucket 400 immediatelyafter driving is started.

The present invention has been made in view of such a subject asdescribed above, and it is an object of the present invention to providea control method and a control apparatus for a construction machine bywhich, even immediately after driving of an arm mechanism is started, aresponse delay of a pump or an increase of a dead zone is suppressed toachieve improvement in the finish accuracy by a working member.

SUMMARY OF INVENTION

In order to attain the object described above, according to the presentinvention, a control method for a construction machine wherein a jointtype arm mechanism provided on a construction machine body is driven bya cylinder type actuator which is connected to a fluid pressure circuithaving a pump, whose delivery pressure is variable in response to anoperation amount by an operation member, and is operated by the deliverypressure from the pump, is characterized in that the delivery pressureof the pump is maintained equal to or higher than a predetermined valuealso when the operation member is in a non-driving position for thecylinder type actuator.

In the control method for a construction machine described above, alsowhen the operation member is in the non-driving position for thecylinder type actuator, the delivery pressure is maintained equal to orhigher than the predetermined value, and consequently, even immediatelyafter the operation member is operated from the non-driving position(immediately after driving is started) in order to operate the jointtype arm mechanism, a sufficient pump delivery pressure is obtained anda response delay of the pump or an increase of the dead zone can besuppressed.

Accordingly, even immediately after driving of the arm mechanism isstarted, deterioration of the posture control accuracy of the workingmember can be prevented, and the finish accuracy by the working membercan be enhanced remarkably.

Meanwhile, a control apparatus for a construction machine of the presentinvention is characterized in that it comprises a construction machinebody, a joint type arm mechanism pivotally mounted at an end portionthereof on the construction machine body and having a working member atthe other end side thereof, a cylinder type actuator mechanism forperforming an expansion/contraction operation to drive the armmechanism, an operation member for operating the arm mechanism throughthe cylinder type actuator mechanism, a fluid pressure circuit having apump whose delivery pressure is variable in response to an operationamount by the operation member for supplying and discharging workingfluid to and from the cylinder type actuator mechanism to cause thecylinder type actuator mechanism to perform an expansion/contractionoperation, detection means for detecting whether or not the operationmember is in a non-driving position for the cylinder type actuatormechanism, and pump control device for maintaining, when it is detectedby the detection means that the operation member is in the non-drivingposition for the cylinder type actuator mechanism, the delivery pressureof the pump equal to or higher than a predetermined value.

It is to be noted that the pump control device described above may beconstructed such that it maintains the delivery pressure of the pumpequal to or higher than the predetermined value if it is detected by thedetection device that the operation member is in the non-drivingposition for the cylinder type actuator mechanism and it is detectedthat a control starting triggering operation by a control startingtriggering operation member has been performed.

Further, the pump control device described above may be constructed suchthat it varies the delivery pressure to be maintained in response to acondition of a load acting upon the cylinder type actuator mechanism,and in this instance, the pump control device may be constructed suchthat it includes storage device in which the maintained deliverypressure to be varied in response to the condition of the load actingupon the cylinder type actuator mechanism.

In the control apparatus for a construction machine of the presentinvention described above, if it is detected by the detection devicedescribed above that the operation member is in the non-driving positionfor the cylinder type actuator mechanism, the delivery pressure of thepump is maintained equal to or higher than the predetermined value bythe pump control device, and consequently, even immediately after theoperation member is operated from the non-driving position (immediatelyafter driving is started) in order to operate the joint type armmechanism, a sufficient pump delivery pressure is obtained and aresponse delay of the pump or an increase of the dead zone can besuppressed.

Accordingly, also in this instance, even immediately after driving ofthe arm mechanism is started, deterioration of the posture controlaccuracy of the working member can be prevented, and the finish accuracyby the working member can be enhanced remarkably.

It is to be noted that, where the pump control device maintains thedelivery pressure of the pump equal to or higher than the predeterminedvalue when it is detected by the detection means described above thatthe operation member is in the non-driving position for the cylindertype actuator mechanism and it is detected that a control startingtriggering operation by the control starting triggering operation memberhas been performed, whether or not the control operation of the pumpcontrol device for maintaining the delivery pressure of the pump equalto or higher than the predetermined value when the operation member isin the non-driving position can be selected by a control startingtriggering operation by the control starting triggering operationmember.

Accordingly, only when an operator or the like wants, the controloperation by the pump control device can be performed, and the deliverypressure of the pump need not be held to an unnecessarily high pressurecondition and efficient operation can be achieved.

Further, where the pump control device varies the delivery pressure tobe maintained in response to a condition of the load acting upon thecylinder type actuator mechanism, an increase of the dead zone whicharises from the fact that the pump load is lower than the load to thecylinder type actuator mechanism can be suppressed with certainty, andconsequently, the control apparatus for a construction machinecontributes very much to enhancement of the finish accuracy by theworking member.

In this instance, where the maintained delivery pressure to be varied inresponse to the condition of the load acting upon the cylinder typeactuator mechanism is stored in advance in the storage means, the pumpcontrol device can obtain an optimum delivery pressure to be maintainedof the pump and perform variation control of the delivery pressure ofthe pump only if it reads out the delivery pressure to be maintainedcorresponding to the condition of the load acting upon the cylinder typeactuator mechanism from the storage device .

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a hydraulic excavator on which a controlapparatus according to an embodiment of the present invention ismounted;

FIG. 2 is a view schematically showing a general construction (electricsystem and hydraulic system) of the control apparatus according to theembodiment of the present invention;

FIG. 3 is a block diagram schematically showing a general constructionof the control apparatus according to the embodiment of the presentinvention;

FIG. 4 is a block diagram for explaining a functional construction ofthe entire control apparatus according to the embodiment of the presentinvention;

FIG. 5 is a control block diagram of essential part of the controlapparatus according to the embodiment of the present invention;

FIG. 6 is a block diagram for explaining a characteristic function ofthe control apparatus according to the embodiment of the presentinvention and construction of essential part relating to the function;

FIG. 7 is a side elevational view showing operating parts (a joint typearm mechanism and a bucket) of the hydraulic excavator according to thepresent embodiment;

FIG. 8 is a side elevational view schematically showing the hydraulicexcavator in order to explain operation of the hydraulic excavatoraccording to the present embodiment;

FIG. 9 is a side elevational view schematically showing the hydraulicexcavator in order to explain operation of the hydraulic excavatoraccording to the present embodiment;

FIG. 10 is a side elevational view schematically showing the hydraulicexcavator in order to explain operation of the hydraulic excavatoraccording to the present embodiment;

FIG. 11 is a side elevational view schematically showing the hydraulicexcavator in order to explain operation of the hydraulic excavatoraccording to the present embodiment;

FIG. 12 is a side elevational view schematically showing the hydraulicexcavator in order to explain operation of the hydraulic excavatoraccording to the present embodiment; and

FIG. 13 is a side elevational view schematically showing a generalconstruction of a conventional hydraulic excavator.

DETAILED DESCRIPTION OF THE INVENTION

In the following, an embodiment of the present invention is describedwith reference to the drawings.

A hydraulic excavator as a construction machine according to the presentembodiment includes, for example, as schematically shown in FIG. 1, anupper revolving unit (construction machine body) 100 with an operatorcab 600 for revolving movement in a horizontal plane on a lowertraveling body 500 which has caterpillar members 500A on the left andright thereof.

A boom (arm member) 200 having one end connected for swinging motion isprovided on the upper revolving unit 100, and a stick (arm member) 300connected at one end thereof for swinging motion by a joint part isprovided on the boom 200.

A bucket working member) 400 which is connected at one end thereof forswinging motion by a joint part and can excavate the ground with a tipthereof and accommodate earth and sand therein is provided on the stick300.

In this manner, a joint type arm mechanism which is mounted at one endportion thereof for pivotal motion on the upper revolving unit 100 andhas the bucket 400 on the other end side thereof and further has theboom 200 and the stick 300 as a pair of arm members connected to eachother by the joint part is composed of the boom 200, stick 300 andbucket 400.

Further, a boom hydraulic cylinder 120, a stick hydraulic cylinder 121and a bucket hydraulic cylinder 122 (in the following description, theboom hydraulic cylinder 120 may be referred to as boom cylinder 120 ormerely as cylinder 120, the stick hydraulic cylinder 121 may be referredto as stick cylinder 121 or merely as cylinder 121, and the buckethydraulic cylinder 122 may be referred to as bucket cylinder 122 ormerely as cylinder 122) as cylinder type actuators are provided.

Here, the boom cylinder 120 is connected at one end thereof for swingingmotion to the upper revolving unit 100 and is connected at the other oneend thereof for swinging motion to the boom 200, or in other words, theboom cylinder 120 is interposed between the upper revolving unit 100 andthe boom 200, such that, as the distance between the opposite endportions is expanded or contracted, the boom 200 can be swung withrespect to the upper revolving unit 100.

The stick cylinder 121 is connected at one end thereof for swingingmotion to the boom 200 and connected at the other one end thereof forswinging motion to the stick 300, or in other words, the stick cylinder121 is interposed between the boom 200 and the stick 300, such that, asthe distance between the opposite end portions is expanded orcontracted, the stick 300 can be swung with respect to the boom 200.

The bucket cylinder 122 is connected at one end thereof for swingingmotion to the stick 300 and connected at the other one end thereof forswinging motion to the bucket 400, or in other words, the bucketcylinder 122 is interposed between the stick 300 and the bucket 400,such that, as the distance between the opposite end portions thereof isexpanded or contracted, the bucket 400 can be swung with respect to thestick 300. It is to be noted that a linkage 130 is provided at a freeend portion of the bucket hydraulic cylinder 122.

In this manner, a cylinder type actuator mechanism having a plurality ofcylinder type actuators for driving the arm mechanism by performingexpanding or contracting operations is composed of the cylinders 120 to122 described above.

It is to be noted that, thoughnot shown in the figure, also hydraulicmotors for driving the left and right caterpillar members 500A and arevolving motor for driving the upper revolving unit 100 to revolve areprovided.

By the way, as shown in FIG. 2, a hydraulic circuit (fluid pressurecircuit) for the cylinders 120 to 122, the hydraulic motors and therevolving motor described above is provided, and in addition to pumps 51and 52 of the variable delivery pressure type which are driven by anengine E, a boom main control valve (control valve) 13, a stick maincontrol valve (control valve) 14, a bucket main control valve (controlvalve) 15 and so forth are interposed in the hydraulic circuit. Thepumps 51 and 52 of the variable delivery pressure type are eachconstructed such that the camp plate angle (tilt angle) is controlled byan engine pump controller 27 which will be hereinafter described so thatthe delivery pressure of working oil to the hydraulic circuit can bevaried.

It is to be noted that, where each line which interconnects differentcomponents is a solid line in FIG. 2, this represents that this line isan electric system, but where each line which interconnects differentcomponents is a broken line, this represents that the line is ahydraulic system.

Further, in order to control the main control valves 13, 14 and 15, apilot hydraulic circuit is provided, and in addition to a pilot pump 50driven by the engine E, solenoid proportional valves 3A, 3B and 3C,solenoid directional switch valves 4A, 4B and 4C, selector valves 18A,18B and 18C and so forth are interposed in the pilot hydraulic circuit.

In the hydraulic excavator of the present embodiment, a controller 1 forcontrolling the main control valves 13, 14 and 15 via the solenoidproportional valves 3A, 3B and 3C to control the boom 200, the stick 300and the bucket 400 in response to a mode in which they should becontrolled so that they may have desired expansion/contractiondisplacements is provided. It is to be noted that the controller 1 iscomposed of a microprocessor, memories such as a ROM and a RAM, suitableinput/output interfaces and so forth.

To the controller 1, detection signals (including setting signals) fromvarious sensors are inputted, and the controller 1 executes the controldescribed above based on the detection signals from the sensors. It isto be noted that such control by the controller 1 is calledsemiautomatic control, and even during excavation under thesemiautomatic control (semiautomatic excavation mode), it is possible tomanually effect fine adjustment of a bucket angle and an aimed slopeface height.

As such a semiautomatic control mode (semiautomatic excavation mode) asdescribed above, a bucket angle control mode (refer to FIG. 8), a slopeface excavation mode (bucket tip linear excavation mode or raking mode;refer to FIG. 9), a smoothing mode which is a combination of the slopeface excavation mode and the bucket angle control mode (refer to FIG.10), a bucket angle automatic return mode (automatic return mode; referto FIG. 11) and so forth are available.

Here, the bucket angle control mode is a mode in which the angle (bucketangle) of the bucket 400 with respect to the horizontal direction(vertical direction) is always kept constant even if the stick 300 andthe boom 200 are moved as shown in FIG. 8, and this mode is executed ifa bucket angle control switch on a monitor panel 10 which will behereinafter described is switched ON. It is to be noted that this modeis cancelled when the bucket 400 is moved manually, and a bucket angleat a point of time when the bucket 400 is stopped is stored as a newbucket holding angle.

The slope face excavation mode is a mode in which a tip 112 (which maysometimes be referred to as bucket tip 112) of the bucket 400 moveslinearly as shown in FIG. 9. However, the bucket cylinder 122 does notmove. Further, the bucket angle φ varies as the bucket 400 moves.

The slope face excavation mode+bucket angle control mode (smoothingmode) is a mode in which the tip 112 of the bucket 400 moves linearlyand also the bucket angle φ is kept constant during excavation as shownin FIG. 10.

The bucket automatic return mode is a mode in which the bucket angle isautomatically returned to an angle set in advance as shown in FIG. 11,and the return bucket angle is set by the monitor panel 10. This mode isstarted when a bucket automatic return start switch 7 on a boom/bucketoperation lever 6 is switched ON. This mode is cancelled at a point oftime when the bucket 400 returns to the angle set in advance.

The slope face excavation mode and the smoothing mode described aboveare entered when a semiautomatic control switch on the monitor panel 10is switched ON and a slope face excavation switch 9 on a stick operationlever 8 is switched ON and besides both or either one of the stickoperation lever 8 and the boom/bucket operation lever 6 is moved. It isto be noted that the aimed slope face angle is set by a switch operationon the monitor panel 10.

Further, in the slope face excavation mode and the smoothing mode, theoperation amount of the stick operation lever 8 provides a bucket tipmoving velocity in a parallel direction to the aimed slope face angle,and the operation amount of the boom/bucket operation lever 6 provides abucket tip moving velocity in the perpendicular direction. Accordingly,if the stick operation lever 8 is moved, then the bucket tip 112 startsits linear movement along the aimed slope face angle, and fineadjustment of the aimed slope face height by a manual operation can beperformed by moving the boom/bucket operation lever 6 during excavation.

Furthermore, in the slope face excavation mode and the smoothing mode,not only the bucket angle during excavation can be adjusted finely, butalso the aimed slope face height can be changed, by operating theboom/bucket operation lever 6.

It is to be noted that, in the present system, also a manual mode ispossible, and in this manual mode, not only operation equivalent to thatof a conventional hydraulic excavator is possible, but also coordinateindication of the bucket tip 112 is possible.

Also a service mode for performing service maintenance of the entiresemiautomatic system is prepared, and this service mode is enabled byconnecting an external terminal 2 to the controller 1. And, by thisservice mode, adjustment of control gains, initialization of varioussensors and so forth are performed.

By the way, as the various sensors connected to the controller 1, asshown in FIG. 2, pressure switches 16, pressure sensors 19, 28A and 28B,resolvers (angle sensors, posture detection means) 20 to 22, a vehicleinclination angle sensor 24 and so forth are provided. Further, to thecontroller 1, the engine pump controller 27, an ON-OFF switch (bucketautomatic return start switch described above) 7, another ON-OFF switch(slope face excavation switch described hereinabove) 9, the monitorpanel (display switch panel) 10 with an aimed slope face angle settingunit are connected. It is to be noted that the external terminal 2 isconnected to the controller 1 upon adjustment of the control gains,initialization of the sensors and so forth.

The engine pump controller 27 receives engine speed information from anengine speed sensor 23 and controls the cam plate angles (tilt angles)of the engine E and the pumps 51 and 52 of the variable deliverypressure type described above. The engine pump controller 27 cancommunicate coordination information with the controller 1. The pressuresensors 19 are attached to pilot pipes connected from the operationlevers 6 and 8 for expansion/contraction of the stick 300 and forupward/downward movement of the boom 200 to the main control valves 13,14 and 15 and detect pilot hydraulic pressures in the pilot pipes. Sincethe pilot hydraulic pressures in such pilot pipes are varied by theoperation amounts of the operation levers 6 and 8, by measuring thehydraulic pressures, the controller 1 can estimate the operation amountsof the operation levers 6 and 8 based on the measured hydraulicpressures.

The pressure sensors 28A and 28B detect expansion/contraction conditionsof the boom cylinder 120 and stick cylinder 121, respectively, and theload conditions acting upon the cylinders 120 and 121 can be detected bythe pressure sensors 28A and 28B, respectively.

It is to be noted that, upon the semiautomatic control described above,the stick operation lever 8 is used to determine the bucket tip movingvelocity in a parallel direction with respect to a set excavation slantface, and the boom/bucket operation lever 6 is used to determine thebucket tip moving velocity in the perpendicular direction with respectto the set slant face. Accordingly, when the stick operation lever 8 andthe boom/bucket operation lever 6 are operated simultaneously, themoving direction and the moving velocity of the bucket tip aredetermined by a composite vector in the parallel and perpendiculardirections with respect to the set slant face.

The pressure switches 16 are attached to the pilot pipes for theoperation levers 6 and 8 for the boom 200, stick 300 and bucket 400 withselector valves 17 or the like interposed therebetween and are used todetect whether or not the operation levers 6 and 8 are in a neutralcondition. In particular, when the operation lever 6 or 8 is in theneutral condition, the output of the pressure switch 16 is OFF, but whenthe operation lever 6 or 8 is used, the output of the pressure switch 16is ON. It is to be noted that the pressure switches 16 for detection ofa neutral condition are used also for detection of an abnormal conditionof the pressure sensors 19 and for switching between themanual/semiautomatic modes.

The resolver 20 is provided at a pivotally mounted portion (joint part)of the boom 200 on the construction machine body 100 at which theposture of the boom 200 can be monitored and functions posture detectionmeans for detecting the posture of the boom 200. The resolver 21 isprovided at a pivotally mounted portion (joint part) of the stick 300 onthe boom 200 at which the posture of the stick 300 can be monitored andfunctions as posture detection means for detecting the posture of thestick 300. Further, the resolver 22 is provided at a linkage pivotallymounted portion at which the posture of the bucket 400 can be monitoredand functions as posture detection means for detecting the posture ofthe bucket 400. By those resolvers 20 to 22, angle detection means fordetecting the posture of the arm mechanism in angle information iscomposed.

A signal converter 26 converts angle information obtained by theresolver 20 into expansion/contraction displacement information of theboom cylinder 120, converts angle information obtained by the resolver21 into expansion/contraction displacement information of the stickcylinder 121, and converts angle information obtained by the resolver 22into expansion/contraction displacement information of the bucketcylinder 122, that is, converts angle information obtained by theresolvers 20 to 22 into corresponding expansion/contraction displacementinformation of the cylinders 120 to 122.

To this end, the signal converter 26 includes an input interface 26A forreceiving signals from the resolvers 20 to 22, a memory 26B whichincludes a lookup table 26B-1 for storing expansion/contractiondisplacement information of the cylinders 120 to 122 corresponding toangle information obtained by the resolvers 20 to 22, a main arithmeticunit (CPU) 26C which can calculate the expansion/contractiondisplacement information of the cylinders 120 to 122 corresponding toangle information obtained by the resolvers 20 to 22 and communicate thecylinder expansion/contraction displacement information with thecontroller 1, and an output interface 26D for sending out the cylinderexpansion/contraction displacement information from the CPU 26C.

The expansion/contraction displacement information λbm, λst and λbk ofthe cylinders 120 to 122 corresponding to the angle information θbm, θstand θbk obtained by the resolvers 20 to 22 described above can becalculated using the cosine theorem in accordance with the followingexpressions (1) to (3):

    λbm=(L.sub.101/102.sup.2 +L.sub.101/111.sup.2 -2L.sub.101/102 ·L.sub.101/111 cos (θbm+Axbm)).sup.1/2     (1)

    λst=(L.sub.103/104.sup.2 +L.sub.104/105.sup.2 -2L.sub.103/104 ·L.sub.104/105 cos θst).sup.1/2            (2)

    λbk=(L.sub.106/107.sup.2 +L.sub.107/109.sup.2 -2L.sub.106/107 ·L.sub.107/109 cos θbk).sup.1/2            (3)

Here, in the expressions above, L_(i/j) represents a fixed length, Axbmrepresents a fixed angle, and the suffix i/j to L has informationbetween the nodes i and j. For example, L_(101/102) represents thedistance between the node 101 and the node 102. It is to be noted thatthe node 101 is determined as the origin of the xy coordinate system(refer to FIG. 7).

Naturally, each time the angle information θbm, θst and θbk is obtainedby the resolvers 20 to 22, the expressions above may be calculated byarithmetic means (for example, the CPU 26C). In this instance, the CPU26C forms the arithmetic means which calculates, based on the angleinformation obtained by the resolvers 20 to 22, expansion/contractiondisplacement information of the cylinders 120 to 122 corresponding tothe angle information by calculation.

It is to be noted that signals obtained by the conversion by the signalconverter 26 are utilized not only for feedback control uponsemiautomatic control but also to measure coordinates formeasurement/indication of the position of the tip 112 of the bucket 400.

The position of the bucket tip 112 (the position may be hereinafterreferred to as bucket tip position 112) in the semiautomatic system iscalculated using a certain point of the upper revolving unit 100 of thehydraulic excavator as the origin. However, when the upper revolvingunit 100 is inclined in the front linkage direction, it is necessary torotate the coordinate system for control calculation by an angle bywhich the vehicle is inclined. The vehicle inclination angle sensor 24is used to correct the coordinate system for an amount of the rotationof the coordinate system.

While the solenoid proportional valves 3A to 3C control the hydraulicpressures supplied from the pilot pump 50 in response to electricsignals from the controller 1 and the controlled hydraulic pressures actupon the main control valves 13, 14 and 15 through the switch valves 4Ato 4C or the selector valves 18A to 18C to control the spool positionsof the main control valves 13, 14 and 15 so that aimed cylindervelocities may be obtained, if the control valves 4A to 4C are set tothe manual mode side, then the cylinders 120 to 122 can be controlledmanually.

It is to be noted that a stick confluence control proportional valve 11adjusts the confluence ratio of the two pumps 51 and 52 in order toobtain an oil amount corresponding to an aimed cylinder velocity.

Further, the ON-OFF switch (slope face excavation switch) 9 describedhereinabove is mounted on the stick operation lever 8, and as anoperator operates the switch 9, a semiautomatic mode is selected or notselected. Then, if a semiautomatic mode is selected, then the tip 112 ofthe bucket 400 can be moved linearly.

Furthermore, the ON-OFF switch (bucket automatic return start switch) 7described hereinabove is mounted on the boom/bucket operation lever 6,and as an operator switches on the switch 7, the bucket 400 can beautomatically returned to an angle set in advance.

Safety valves 5 are provided to switch the pilot pressures to besupplied to the solenoid proportional valves 3A to 3C, and only when thesafety valves 5 are in an ON state, the pilot pressures are supplied tothe solenoid proportional valves 3A to 3C. Accordingly, when somefailure occurs or in a like case in the semiautomatic control, automaticcontrol of the linkage can be stopped rapidly by switching the safetyvalves 5 to an OFF state.

The speed of the engine E is different depending upon the position ofthe engine throttle set by an operator [the position is set by operatinga throttle dial (not shown)], and further, even if the position of theengine throttle is fixed, the engine speed varies depending upon theload. Since the pumps 50, 51 and 52 are directly connected to the engineE, if the engine speed varies, then also the pump discharges (pumpdelivery pressures) vary, and consequently, even if the spool positionsof the main control valves 13, 14 and 15 are fixed, the cylindervelocities are varied by the variation of the engine speed. In order tocorrect this, the engine speed sensor 23 is mounted, and when the enginespeed is low, the aimed moving velocity of the tip 112 of the bucket 400is set slow.

The monitor panel 10 with an aimed slope face angle setting unit (whichmay sometimes be referred to simply as monitor panel 10) is not onlyused as a setting unit for the aimed slope face angle α (refer to FIGS.7 and 12) and the bucket return angle, but also used as an indicator forcoordinates of the bucket tip 12, the slope face angle measured or thedistance between coordinates of two points measured. It is to be notedthat the monitor panel 10 is provided in the operator cab 600 togetherwith the operation levers 6 and 8.

In particular, in the system according to the present embodiment, thepressure sensors 19 and the pressure switches 16 are incorporated inconventional pilot hydraulic lines to detect operation amounts of theoperation levers 6 and 8 and feedback control is effected using theresolvers 20, 21 and 22 while multiple freedom degree feedback controlcan be effected independently for each of the cylinders 120, 121 and122. Consequently, the requirement for addition of an oil unit such as apressure compensation valve is unnecesary. Further, an influence ofinclination of the upper revolving unit 100 is corrected using thevehicle inclination angle sensor 24, and the solenoid proportionalvalves 3A to 3C are utilized in order to drive the cylinders 120, 121and 122 with electric signals from the controller 1. It is to be notedthat an operator can select a mode arbitrarily using themanual/semiautomatic mode change-over switch 9 and besides can set anaimed slope face angle.

In the following, a control algorithm of the semiautomatic systemperformed by the controller 1 is described. The control algorithm of thesemiautomatic control mode (except the bucket automatic return mode)effected by the controller 1 is substantially such as illustrated inFIG. 4.

In particular, the moving velocity and the moving direction of the tip122 of the bucket 400 are first calculated based on information of theaimed slope face set angle, the pilot hydraulic pressures forcontrolling the stick cylinder 121 and the boom cylinder 120, thevehicle inclination angle and the engine speed. Then, aimed velocitiesof the cylinders 120, 121 and 122 are calculated based on the calculatedinformation (moving velocity and moving direction of the tip 112 of thebucket 400). In this instance, the information of the engine speed isrequired to determine an upper limit to the cylinder velocities.

Further, the controller 1 includes, as shown in FIGS. 3 and 4, controlsections 1A, 1B and 1C provided independently of each other for thecylinders 120, 121 and 122, and the controls are constructed asindependent control feedback loops as shown in FIG. 4 so that they maynot interfere with each other.

Here, essential part of the control apparatus of the present embodimentis described. The compensation construction in the closed loop controlsshown in FIG. 4 has, in each of the control sections 1A, 1B and 1C, amultiple freedom degree construction including a feedback loop and afeedforward, loop with regard to the displacement and the velocity asshown in FIG. 5, and includes feedback loop type compensation means 72having a variable control gain (control parameter), and feed forwardloop type compensation means 73 having a variable control gain (controlparameter).

In particular, if an aimed velocity is given, then feedback loopprocesses according to a route wherein a deviation between the aimedvelocity and velocity feedback information is multiplied by apredetermined gain Kvp (refer to reference numeral 62), another routewherein the aimed velocity is integrated once (refer to an integrationelement 61 of FIG. 5) and a deviation between the aimed velocityintegration information and displacement feedback information ismultiplied by a predetermined gain Kpp (refer to reference numeral 63)and a further route wherein the deviation between the aimed velocityintegration information and the displacement feedback information ismultiplied by a predetermined gain Kpi (refer to reference numeral 64)and further integrated (refer to reference numeral 66) are performed bythe feedback loop type compensation means 72 while, by the feedforwardloop type compensation means 73, a feedforward loop process by a routewherein the aimed velocity is multiplied by a predetermined gain Kf(refer to reference numeral 65) is performed.

Of the processes mentioned, the feedback loop processes are described inmore detail. The present apparatus includes, as shown in FIG. 5,operation information detection means 91 for detecting operationinformation of the cylinders 120 to 122, and the controller 1 receivesthe detection information from the operation information detection means91 and aimed operation information (for example, an aimed movingvelocity) set by aimed value setting means 80 as input information andsets and outputs control signals so that the arm members such as theboom 200 and the bucket (working member) 400 may exhibit aimed operationconditions. Further, the operation information detection means 91particularly is cylinder position detection means 83 which can detectpositions of the cylinders 120 to 122, and in the present embodiment,the cylinder position detection means 83 is composed of the resolvers 20to 22 and the signal converter 26 described hereinabove.

It is to be noted that the values of the gains Kvp, Kpp, Kpi and Kf canbe changed by a gain scheduler 70.

Further, while a non-linearity removal table 71 is provided to removenon-linear properties of the solenoid proportional valves 3A to 3C, themain control valves 13 to 15 and so forth, a process in which thenon-linearity removal table 71 is used is performed at a high speed by acomputer by using a table lookup technique.

By the way, in the control apparatus of the present embodiment, theengine pump controller 27 and the controller 1 cooperate with each otherto provide functions of variably controlling the delivery pressures ofthe pumps 51 and 52 (functions as pump control means). Main ones of thefunctions are a function 1 and another function 2 described below:

Function 1): function of variably controlling the delivery pressures ofthe pumps 51 and 52 in response to an operation amount by the stickoperation lever (operation member) 8. The function of controlling, whenthe operation lever 6 or 8 is operated from a condition (idlingcondition) wherein the operation lever 6 or 8 is disposed at its neutralposition (non-driving position) and the pumps 51 and 52 little deliverthe working oil, the cam plate angles of the pumps 51 and 52 so that thedelivery pressures of the pumps 51 and 52 may gradually rise in responseto the operation amount of the operation lever 6 or 8.

Function 2: function of controlling the cam plate angles of the pumps 51and 52 so that the delivery pressures of the angle pumps 51 and 52 maybe held equal to or higher than a predetermined value (to a highpressure condition) in response to a control starting triggeringoperation by a pushbutton switch 8a (refer to FIG. 6) provided for thestick operation lever 8, a signal from a neutral position detectingsensor (detection means) 8b for detecting whether or not the stickoperation lever 8 is in a non-driving position (neutral position; in aposition in which the pumps 51 and 52 are in an idling condition) forthe cylinders 120 and 121 and signals from the pressure sensors 28A and28B (load conditions of the cylinders 120 and 121). More particularly,the function of controlling, when the stick operation lever 8 is in itsneutral position and the pushbutton switch 8a is depressed, the camplate angles of the pumps 51 and 52 so that delivery pressurescorresponding to the load conditions of the cylinders 120 and 121 may bemaintained.

The latter function 2 which is a characteristic function of the presentinvention is described in more detail with reference to FIG. 6.

As shown in FIG. 6, in the present embodiment, the neutral positiondetecting sensor (detection means) 8b for detecting whether the stickoperation lever 8 is in its non-driving position (neutral position) forthe cylinders 120 and 121 and the pushbutton switch (control startingtriggering operation member) 8a which is operated when semiautomaticcontrol is to be started are provided for the stick operation lever 8.

The controller 1 has a pump cam plate angle setting table (storagemeans) which will be hereinafter described, and when it is detected bythe neutral position detecting sensor 8b that the stick operation lever8 is in its neutral position and the pushbutton switch 8a is depressed(control starting triggering operation), the controller 1 outputs a pumpcam plate instruction value to the engine pump controller 27 to controlthe delivery pressures of the cylinders 120 and 121 so that the deliverypressures may be held at delivery pressures (high pressure condition)corresponding to the load conditions of the cylinders 120 and 121(maximum values of the cylinder load pressures) detected by the pressuresensors 28A and 28B.

Then, the engine pump controller 27 which receives the pump cam plateinstruction value from the controller 1 actually performs control of thepumps 51 and 52 by adjusting them so that the cam plate angles of themmay be equal to the pump cam plate instruction to maintain the deliverypressures of the pumps 51 and 52 equal to or higher than thepredetermined value.

The pump cam plate angle setting table 60 is provided to output a pumpcam plate angle (pump cam plate instruction value) corresponding to theload conditions of the cylinders 120 and 121 (maximum values of theloads in the cylinder driving direction) detected by the pressuresensors 28A and 28B, and is stored in a memory (for example, a ROM or aRAM), which composes the controller 1, in advance to allow a pump camplate angle corresponding to a maximum value of a cylinder load pressureto be read out by using a table lookup technique.

In the pump cam plate angle setting table 60, the pump cam plate angleis set such that the delivery pressure of each of the pumps 51 and 52increases as the maximum values of the cylinder load pressures detectedby the pressures sensors 28A and 28B increase as shown, for example, inFIG. 6.

It is to be noted that, while, in the present embodiment, the pushbuttonswitch 8a as a control starting triggering operation member and theneutral position detecting sensor 8b are provided for the stickoperation member 8, they may be provided for the boom/bucket operationlever 6. Further, while, in the present embodiment, the pump cam plateangle setting table 60 and the function of outputting a pump cam plateinstruction value based on the table 60 are provided in the controller 1the table 60 and the pump cam plate instruction value outputtingfunction may be provided in the engine pump controller 27.

In the present embodiment having such a construction as described above,when such a slope face excavating operation of an aimed slope face anglea as shown in FIG. 12 is performed semi-automatically using thehydraulic excavator, in the system according to the present invention,such semiautomatic control functions as described above can be realizedby an electronic hydraulic system which automatically adjusts thecomposite moving amount of the boom 200 and the stick 300 in accordancewith the excavating velocity in contrast with a conventional system ofmanual control.

In particular, detection signals (including setting information of anaimed slope face angle) are inputted from the various sensors to thecontroller 1 mounted on the hydraulic excavator, and the controller 1controls the main control valves 13, 14 and 15 through the solenoidproportional valves 3A, 3B and 3C based on the detection signals fromthe sensors (including detection signals of the resolvers 20 to 22received via the signal converter 26) to effect such control that theboom 200, stick 300 and bucket 400 may exhibit desiredexpansion/contraction displacements to effect such semiautomatic controlas described above.

Then, upon the semiautomatic control, the moving velocity and the movingdirection of the tip 112 of the bucket 400 are calculated frominformation of the aimed slope face set angle, the pilot hydraulicpressures which control the stick cylinder 121 and the boom cylinder120, the vehicle inclination angle and the engine speed, and aimedvelocities of the cylinders 120, 121 and 122 are calculated based on thecalculated information (moving velocity and moving direction of the tip112 of the bucket 400). In this instance, an upper limit to the cylindervelocities is determined based on the information of the engine speed.Further, the controls are performed as the feedback loops independent ofeach other for the cylinders 120, 121 and 122 and do not interfere witheach other.

Particularly in the control apparatus of the present embodiment, when itis detected by the neutral position detecting sensor 8b that the stickoperation lever 8 is in its neutral position and it is detected that adepression operation of the pushbutton switch 8a has been performed, apump cam plate angle corresponding to the maximum value of the cylinderload pressures is read out from the pump cam plate angle setting table60 by the controller 1 and outputted as a pump camplate instructionvalue to the engine pump controller 27 as described above with referenceto FIG. 6.

Consequently, the cam plate angles of the pumps 51 and 52 which are in acondition immediately before starting of driving of the system areadjusted by the engine pump controller 27 so that the delivery pressuresthereof are controlled so as to be maintained equal to or higher than apredetermined delivery pressure corresponding to the maximum value ofthe cylinder load pressures.

It is to be noted that the setting of the aimed slope face angle in thesemiautomatic system can be performed by a method which is based oninputting of a numerical value by switches on the monitor panel 10, atwo point coordinate inputting method, or an inputting method by abucket angle, and similarly, for the setting of the bucket return anglein the semiautomatic system, a method which is based on inputting of anumerical value by the switches on the monitor panel 10 or a methodwhich is based on bucket movement is performed. For all of them, knowntechniques are used.

Further, the semiautomatic control modes described above and thecontrolling methods are performed in the following manner based oncylinder expansion/contraction displacement information obtained byconversion by the signal converter 26 of the angle information detectedby the resolvers 20 to 22.

First, in the bucket angle control mode, the length of the bucketcylinder 122 is controlled so that the angle (bucket angle) φ definedbetween the bucket 400 and the x axis may be fixed at each arbitraryposition. In this instance, the bucket cylinder length λbk is determinedif the boom cylinder length λbm, the stick cylinder length λst and theangle φ mentioned above is determined.

In the smoothing mode, since the bucket angle φ is kept fixed, thebucket tip position 112 and a node 108 move inparallel. First, a casewherein the node 108 moves in parallel to the x axis (horizontalexcavation) is considered. In particular, in this instance, thecoordinates of the node 108 in the linkage posture when excavation isstarted are represented by (x₁₀₈, y₁₀₈), and the cylinder lengths of theboom cylinder 120 and the stick cylinder 121 in the linkage posture inthis instance are calculated and the velocities of the boom 200 and thestick 300 are calculated so that x₁₀₈ may move horizontally. It is to benoted that the moving velocity of the node 108 depends upon theoperation amount of the stick operation lever 8.

On the other hand, where parallel movement of the node 108 isconsidered, the coordinates of the node 108 after the very short time Atare represented by (x₁₀₈ +Δx, y₁₀₈). Δx is a very small displacementwhich depends upon the moving velocity. Accordingly, by taking Δx intoconsideration of x₁₀₈, aimed lengths of the boom and stick cylindersafter Δt can be calculated.

In the slope face excavation mode, control similar to that in thesmoothing mode may be performed. However, the point which moves ischanged from the node 108 to the bucket tip position 112, and further,the control takes it into consideration that the bucket cylinder lengthis fixed.

Further, in correction of a finish inclination angle by the vehicleinclination sensor 24, calculation of the front linkage position isperformed on the xy coordinate system whose origin is a node 101 of FIG.7. Accordingly, if the vehicle body is inclined with respect to the xyplane, then the xy coordinates are rotated, and the aimed inclinationangle with respect to the ground surface is varied. In order to correctthis, the vehicle inclination angle sensor 24 is mounted on the vehicle,and when it is detected by the vehicle inclination angle sensor 24 thatthe vehicle body is rotated by β with respect to the xy plane, the aimedinclination angle should be corrected by replacing it with a valueobtained by adding β to it.

Prevention of deterioration of the control accuracy by the engine speedsensor 23 is such as follows. In particular, with regard to correctionof the aimed bucket tip velocity, the aimed bucket tip velocity dependsupon the positions of the operation levers 6 and 8 and the engine speed.Meanwhile, since the hydraulic pumps 51 and 52 are directly connected tothe engine E, when the engine speed is low, also the pump discharges aresmall and the cylinder velocities are low. Therefore, the engine speedis detected, and the aimed bucket tip velocity is calculated so as toconform with the variation of the pump discharges.

Meanwhile, with regard to correction of the maximum values of the aimedcylinder velocities, correction is performed taking it intoconsideration that the aimed cylinder velocities are varied by theposture of the linkage and the aimed slope face inclination angle andthat, when the pump discharges decrease as the engine speed decreases,also the maximum cylinder velocities must be decreased. It is to benoted that, if an aimed cylinder velocity exceeds its maximum cylindervelocity, then the aimed bucket tip velocity is decreased so that theaimed cylinder velocity may not exceed the maximum cylinder velocity.

While the various control modes and the controlling methods aredescribed above, they all employ a technique wherein they are performedbased on cylinder expansion/contraction displacement information, andcontrol contents according to this technique are publicly known. Inparticular, in the system according to the present embodiment, sinceangle information is detected by the resolvers 20 to 22 and then theangle information is converted into cylinder expansion/contractiondisplacement information by the signal converter 26, the knowncontrolling technique can be used for later processing.

While the various controls are performed by the controller 1 in thismanner, in the system according to the present embodiment, since, afterthe pushbutton switch 8a is depressed but immediately before driving ofthe system is started (for example, immediately before automatic controlof linear excavation is started), the cam plate angles are adjusted sothat the delivery pressures of the pumps 51 and 52 may conform tomaximum values of the loads in the cylinder driving direction and thedelivery pressures may be held in a high pressure condition, evenimmediately after the stick operation lever 8 is operated from itsneutral position in order to operate the joint type arm mechanism,sufficient pump delivery pressures are obtained and response delays ofthe pumps or an increase of the dead zone can be suppressed withcertainty. Accordingly, even immediately after driving of the armmechanism is started, deterioration of the posture control accuracy ofthe bucket 400 can be prevented, and the finish accuracy of ahorizontally leveled surface or the like by the bucket 400 is enhancedremarkably.

In this instance, since, in the present embodiment, it can be selectedby an operation of the pushbutton switch 8a whether or not a controllingoperation by the function 2 described hereinabove should be performed, acontrolling operation by the function 2 can be performed only when anoperator or the like wants, and the delivery pressure of each of thepumps 51 and 52 need not be held to an unnecessarily high pressurecondition. Consequently, there is an advantage also in that efficientoperation of the system can be achieved.

Further, since, in the present embodiment, the delivery pressures to bemaintained are varied in response to the load conditions (maximum valuesof the cylinder load pressures) acting upon the cylinders 120 and 121 bythe controller 1 (engine pump controller 27), an increase of the deadzone which arises from the fact that the pump load is lower than theloads to the cylinders 120 and 121 can be suppressed with a higherdegree of certainty, and the present invention contributes to furtherenhancement of the finish accuracy of a horizontally leveled surface orthe like by the bucket 400.

In this instance, where the maintained delivery pressures to be variedare stored as the table 60 in accordance with the maximum value of thecylinder load pressure in advance, there is an advantage also in that,only if the delivery pressure to be maintained corresponding to themaximum values of the cylinder load pressures is read out from the table60, the controller 1 can obtain optimum delivery pressures to bemaintained of the pumps 51 and 52 and perform variation control of thedelivery pressures of the pumps 51 and 52.

Meanwhile, with the system according to the present embodiment, sinceangle information signals detected by the resolvers 20 to 22 areconverted into cylinder displacement information by the signal converter26 and then inputted to the controller 1, control in which cylinderexpansion/contraction displacements which are used in a conventionalcontrol system are used can be executed even if an expensive strokesensor for detecting an expansion/contraction displacement of each ofthe cylinders for the boom 200, stick 300 and bucket 400 as in the priorart is not used. Consequently, while the cost is suppressed low, asystem which can control the position and the posture of the bucket 400accurately and stably can be provided.

Further, since the feedback control loops are independent of each otherfor the cylinders 120, 121 and 122 and the control algorithm ismulti-degree-of-freedom control of the displacement, velocity andfeedforward, the control system can be simplified. Further, since thenon-linearity of a hydraulic apparatus can be converted into linearityat a high speed by a table lookup technique, the present systemcontributes also to augmentation of the control accuracy.

Furthermore, since deterioration of the control accuracy by the positionand load variations of the engine throttle is corrected by correctingthe influence of the vehicle inclination by the inclination angle sensor24 or reading in the engine speed, the present system contributes torealization of more accurate control.

Further, since also maintenance such as gain adjustment can be performedusing the external terminal 2, also an advantage that adjustment or thelike is easy can be obtained, and furthermore, since operation amountsof the operation levers 6 and 8 are determined based on variations ofthe pilot pressures using the pressure sensors 19 and so forth andbesides a conventional open center valve hydraulic system is utilized asit is, there is an advantage that addition of a pressure compensationvalve or the like is not required, and also it is possible to displaythe bucket tip coordinates on the real time basis on the monitor panel10 with an aimed slope face angle setting unit. Further, due to theconstruction which employs the safety valve 5, also an abnormal systemoperation when the system is abnormal can be prevented.

It is to be noted that, while it is described in the embodimentdescribed above that the present invention is applied to a hydraulicexcavator, the present invention is not limited to this. The presentinvention can be applied similarly to a construction machine such as atractor, a loader or a bulldozer only if the construction machine has ajoint type arm mechanism which is driven by cylinder type actuators, andin any construction machine, similar effects to those described abovecan be obtained.

Further, while it is described in the embodiment described above thatthe fluid pressure circuit which operates the cylinder type actuators isa hydraulic circuit, the present invention is not limited to this, andany fluid pressure circuit which utilizes a liquid pressure other thanworking oil or a pneumatic pressure may be used only if it has a pumpwhose delivery pressure can be varied in response to an operation amountby an operation member, and also in this instance, similar operationsand effects to those of the embodiment described above can be achieved.

Furthermore, while it is described in the embodiment described abovethat the engine E is, for example, a Diesel engine, the presentinvention can employ a prime mover (any of various internal combustionengines and so forth) only if it can drive a pump which causes adelivery pressure to act upon a fluid pressure circuit, and the engine Eis not limited to a Diesel engine or the like.

And, the present invention is not limited to the embodiment describedabove and can be carried out in various modified forms without departingfrom the spirit of the present invention.

As described above, according to the present invention, since, evenimmediately after driving of an arm mechanism of a construction machineis started, deterioration of the posture control accuracy of a workingmember can be prevented and the finish accuracy of a horizontallyleveled surface or the like by the working member is enhancedremarkably, a control apparatus for a construction machine of thepresent invention contributes very much to reduction of the workingperiod and so forth in a desired working site such as a constructionsite, and it is considered that the usefulness of the control apparatusfor a construction machine is very high.

What is claimed is:
 1. A control method for a construction machineincluding (i) a joint type arm mechanism, (ii) a cylinder type actuatorbeing operatively connected to a hydraulic circuit to drive the jointtype arm mechanism, and (iii) a pump disposed in the hydraulic circuitand operable to vary delivery pressure in response to a request of anoperator via an operation member, the cylinder type actuator beingoperable to actuate the joint type arm machine and driven by using thedelivery pressure of the pump, said method comprising:(a) detectingwhether the operation member is set at a neutral position in which adriving force of the pump is no longer transmitted to the cylinder typeactuator; (b) triggering, in response to a request, of the operator, acontrol signal to vary the delivery pressure of the pump; (c) monitoringa current value of loading at the cylinder type actuator; and (d)maintaining, if the operation member is set in said neutral position asthe result of said detecting and in respond to said triggering, thedelivery pressure of the pump at a level equal to or higher than atleast one reference pressure value selected from various referencepressure values, in accordance with said monitored value of loading atthe cylinder type actuator.
 2. A control apparatus for a constructionmachine including (i) a construction main body, (ii) a joint type armmechanism pivotally connected at one end to the construction machinebody and having a working member at the other end portion, (iii) acylinder type actuator mechanism, operatively connected with the jointtype arm mechanism, for actuating the joint type arm mechanism extendingand shrinking action of the actuator, (iv) an operation member, to beoperated by the operator for operating the joint type arm mechanism viacylinder type actuator mechanism, (v) a hydraulic circuit having a pumpbeing operable to vary delivery pressure to extend and shrink thecylinder type actuator upon receipt a request of the operator via theoperation member, said control apparatus comprising:(a) a detectingdevice for detecting whether the operation member is set at a neutralposition in which a driving force of the pump is no longer transmittedto the cylinder type actuator; (b) a triggering device for triggering,in response to a request of the operator, a control signal to vary thedelivery pressure of the pump; (c) a monitoring device for monitoring acurrent value of loading at the cylinder type actuator; and (d) a pumpcontrol device, operable if the operation member is set in said neutralposition as the result of detection by said detecting device andresponsive to the triggering by said triggering device, for maintainingthe pressure value of said pump equal to or higher than at least onereference pressure value selected from various reference pressurevalues, in accordance with said current value of loading monitored atsaid monitoring device.
 3. A control apparatus for a constructionmachine as set forth in claim 2, wherein said pump control deviceincludes a storage device for storing various reference pressure valuesfrom which said at least one reference pressure value is to be selectedby said pump control device.